With the development of a diversity of display devices such as a liquid crystal display (LCD), a touch screen has become popular as one of the most efficient input devices for use in facilitating an interface between a display device and a user. The touch screen enables a user to easily manipulate a variety of devices, for example, a computer, a mobile phone, a banking terminal, a game console, etc. using the user's finger or a touch pen while viewing the touch screen, and thus its applications are wide.
Generally, methods for implementing a touch screen include an electrical method and an optical method. The electrical scheme may provide a resistive film type touch screen or an electrostatic capacity type touch screen. The resistive film type and the electrostatic capacity type touch screens increase in cost and have more technical problems as the size is increased, and thus they are usually manufactured as small touch screens.
The optical method may use an infrared matrix, a camera, or the like. The infrared matrix may be used for a medium/large touch screen. However, as a size of the touch screen becomes larger, power consumption and cost are increased and more malfunctions occur due to environmental conditions such as sunlight and lighting.
A camera-based touch screen may calculate location coordinates of a touching object on the basis of angles of images of the touching object captured by two cameras. Similar to the infrared matrix-based touch screen, the camera-based touch screen may have malfunction problems due to the environmental conditions such as sunlight, lighting, and the like. In addition, the angles of the images of the touching object captured by each camera may be inaccurate due to measurement errors caused by distortion of camera lenses. Further, in detecting two or more touches in the touch screen, it is difficult to identify a calculative ghost point, if any.